Miniature antenna for beacons



NOV. 17, 1970 s, DODINGTQN EI'AL 3,541,562

MINIATURE ANTENNA FOR BEACONS ,F iled July 31, 1968 l6 INVENTORS sveu ooonvarcw trluwe c. L. FAY/7M0 BY ERNEST G. PARKER -JAME$ r. wH/r new United States Patent Office 3,541,562 Patented Nov. 17, 1970 US. Cl. 343-760 7 Claims ABSTRACT OF THE DISCLOSURE An inverse mode Tacan antenna includes a cylindrical radiator mounted above a ground plane. A coaxial dielectric cylinder which fits over the radiator is driven by the shaft of a motor positioned inside the radiator. The dielectric cylinder has directors and reflectors attached thereto which change the field of the radiator into a cardioid field. RF. power is coupled to the raditor through a coaxial transmission line whose hollow center conductor is used to carry AC currents to and from the motor. An alternator is assembled within the motor housing and its output is used to provide a phase reference for received signals.

BACKGROUND OF THE INVENTION 5 This invention relates to a miniature antenna and more particularly one capable of providing a rotating field for use, for example, in beacons.

Air rescue systems or systems designed for the purpose of locating mobile or stationary transmitters have been proposed, in which the craft that is being sought ends out a signal which is processed at the searching craft to determine the direction of propagation of the signals.

In one such system, the receiving antenna on the searching craft exhibits a rotating cardioid field pattern which imposes a sinusoidal amplitude modulation upon the received signal, the phase of said modulation being dependent upon the direction from which the signal is being received. When the receiving antenna is pointing in the direction of the transmitter, the modulated signal is at its maximum.

By comparing the received signal with a reference signal synchronized with the rotating field pattern, the bearing of the transmitting antenna can be determined.

Antennas capable of generating rotating field patterns to implement systems as above discussed, are generally heavy and bulky and thus limit the mobility of the receiving system,

An object of the present invention is to provide a relatively light and highly compact antenna arrangement providing a rotating directional pattern suitable for mobile use, such as, on the surface of an aircraft.

SUMMARY OF THE INVENTION According to the invention, a miniature antenna comprising, a hollow monopole antenna, a motor mounted inside said monopole, a rotatable member mounted outside said monopole and means for modifying the field pattern of said monopole including at least one parasitic element mounted on said rotatable member for rotation therewith.

BRIEF DESCRIPTION OF THE DRAWINGS The above-mentioned and other objects of this invention will become apparent by reference to the following description in conjunction with the accompanying drawings in which:

FIG. 1 is a schematic drawing, partially in section, of a miniature airborne antenna;

FIG. 2 is a schematic diagram illustrating a director and reflector supporting structure.

DESCRIPTION OF THE PREFERRED EMBODIMENT In a preferred embodiment, illustrated in FIG. 1, a hollow cylindrical, monopole antenna element 9 is mounted above a ground plane 15 on a dielectric supporting ring 3. Within the hollow portion of said monopole antenna element 9 there is positioned a motor-generator unit 14 whose upwardly directed shaft 14 is connected, via a supporting shaped plate 12 to a dielectric cylinder 11.

The dielectric cylinder 11 supports parasitic elements, further denominated as directors 17 and reflectors 16 and are illustrated in FIG. 2. The reflectors 16 are connected to each other electrically via a ring conductor 13 and are coupled capacitively thereby to a ground plane conductive plate 15 when the antenna is fully assembled as illustrated in FIG. 1.

When an RF. signal is connected to the monopole, a cardioid field pattern is produced by the antenna due to the presence of directors 17 and reflectors 16. When the dielectric structure supporting the above mentioned refiectors 16 and director 17 is rotated, a rotating cardioid field pattern is produced.

RF. signals are coupled to an RF. output connector 4 from the monopole antenna element 9 through a coaxial line 7 having a hollow center conductor 6 which line is shorted at one end by a shorting plate 2. The RF. connector 4 is located at a distance from the shorting plate 2 equal to a quarter wavelength at the midpoint of the operating frequency, The monopole element 9 is electrically connected to the hollow center conductor 6 of the coaxial line 7 by a plate-like conductor 8.

The motor-generator unit 10 is seated inside of the monopole element 9 and is electrically connected to a connector 1 by wires '5 contained within the hollow center conductor 6 of the coaxial line 7. The previously mentioned wires 5 deliver AC currents to the motor and transmit from the generator portion of said motor-generator unit, signals dependent upon the angle of rotation of the shaft of the motor 14. This information is useful in that it may be used as a reference signal to determine the direction of propagation of received signals and therefore a bearing.

We claim:

1. A miniature antenna comprising:

a hollow monopole antenna,

a motor mounted inside said monopole antenna,

a rotatable member mounted outside said monopole;

and

means for modifying the field pattern of said monopole antenna including at least one parasitic element mounted on said rotatable member for rotation therewith.

2. A minature antenna according to claim 1 in which said monopole antenna is cylindrical.

3. A miniature antenna according to claim 2 in which said rotatable member is a section of a dielectric cylinder mounted coaxially with said monopole.

4. A miniature antenna according to claim 1 wherein said means includes parasitic elements comprising reflectors and directors.

5. A miniature antenna according to claim 1 further including a generator combined with said motor in a single unit.

6. A miniature airborne antenna according to claim 5 further including:

a ground plane member,

means for coupling signals to said monopole compris- 4 a coaxial transmission line having a hollow center transmitting means coupled from said connector to the conductor and shorted at one end; motor-generator unit via the hollow center conductor of a RP. connector coupled to said transmission line said coaxial transmission line.

at a predetermined distance from the shorted end; References Cited means for coupling the said center conductor to 5 UNITED STATES PATENTS the monopole antenna element; and 3 054 107 9/1962 En gel et al 343-761 means for coupling the outer conductor to sald 3,191,177 6/1965 Parzen 343 766 ground plane.

7. A miniature airborne antenna according to claim 10 ELI LIEBERMAN Primary Examiner 6 further including means for coupling signals to the motor-generator unit comprising a connector coupled to US. Cl. X.R. the shorted end of said coaxial transmission line, and 343-761, 766, 839 

